The present invention relates to equipment for measuring the electrical characteristics of vacuum tubes.
A common type of radio frequency amplifier has an output stage with two triode vacuum tubes connected in parallel. Each of these tubes is capable of handling several kilowatts of power. In the parallel arrangement, it is important that the tubes have as closely matched performance characteristics as possible.
A standard technique for characterizing vacuum tubes is known as single point static characterization in which the parameters of the tube are measured during operation at a constant relatively low power level. This technique measures the grid current, anode current, anode to cathode voltage, and grid to cathode voltage as indicating the performance of the tube. After measuring the characteristics of a number of tubes, the tubes are grouped in pairs with closely matching parameters.
Utilizing a single operating point to measure the tube parameters does not provide a good indication of the overall tube performance throughout its entire dynamic operating range. For example, the performance of a pair of tubes matched in this manner can differ significantly at higher power levels, so as to adversely affect a signal being amplified in critical applications, such as magnetic resonance imaging equipment
Therefore, it is desirable to measure the performance of the vacuum tube throughout its entire dynamic operating range. However conventional test equipment apply excitation potentials to the tube for relatively long intervals in order to measure the operating parameters. Although tubes are able to tolerate lengthy excitation at low power levels, they often can not withstand continuous high power operation for the required measurement interval. Thus conventional methods for characterizing vacuum tube performance can not measure the operational parameters at high power levels.